Hitherto, when imaging an object, an image has been acquired by using film, a CCD or other such imaging element, an imaging tube, and so forth, placed at the focal plane of various imaging lenses that include telephoto lens.
However, with the conventional technology, when the distance to the object changes it is necessary to change the focal point position, but the focal depth of the camera is limited, and it is difficult to image objects existing in a wide range of distance at a single focal point position. The depth of field can be deepened by deepening the focal depth of the lens. A simple method of deepening the depth of field of a camera is the aperture reduction method, but reducing the aperture degrades the resolution and reduces the intensity of the incident light, so it cannot be used on cameras that are used in dark environments in particular. Moreover, a close distance object cannot be focused unless the focal point position is shifted considerably, and even if it is focused, the depth of field decreases by the square of the shortness in distance, so it is difficult to view a wide range of distance at a close distance. With respect to depth of field, this has been a well-known limitation since before.
As a new method of deepening the depth of field, there is proposed an optical plate that increasingly delays the phase going from the center to the periphery.
For example, Patent Reference 1 (unexamined Japanese patent publication Hei 11-6966) discloses a telescopic system in which, in a Galileo telescope that combines a convex lens comprising an object lens system and a concave lens comprising an eyepiece system, distortion is induced by imparting spherical aberration to the concave lens so that the curvature at the aperture plane of the telescope decreases as the distance from the optical axis increases, producing a special non-diffractive beam that has a narrower width than the optical intensity distribution of the diffraction limit. The object of this was to produce a propagating non-diffractive beam that maintains the condensed light beam at a substantially constant width, and in which, at the same time, the resolution is at or above the resolution of the diffraction limit.
In Patent Reference 2 (unexamined Japanese patent publication 2004-77914), there is disclosed 1) a telescope comprised by combining an object optical system that uses a convex lens, a concave mirror or optical element equivalent to a convex lens, and an eyepiece optical system that uses a concave lens or optical element equivalent to a concave lens, or 2) a structure in which a wavefront control plate that controls the shape of a wavefront is provided in front of an eye or imaging camera having the function of deepening the depth of field of the eye or imaging camera, each 1) and 2) having a characteristic feature that by means of an imaging device and the optical system thereof, the phase of a light wave is delayed according to the distance from the optical axis, and as a result, the curvature in the wavefront of the image-forming light becomes smaller going from the optical axis to the aperture open end, or the phase of a light wave is delayed according to the distance from the aperture open end to the optical axis, and as a result, the curvature in the wavefront of the image-forming light becomes larger going from the aperture end to the optical axis.